1. Field of the Invention
This invention relates generally to the development of interactive visual media, and, more specifically, to improvements in systems used in the development (“authoring”) of media content for delivery in the DVD-Video, Video CD, and similar formats.
2. Background Information
The DVD-Video format is one of a number of formats, both standardized and proprietary, within the general category of interactive multimedia. These formats are capable of presenting motion or still images to an end-user (viewer) on a display such as a television screen or a computer monitor, along with accompanying sound. The media are referred to as “interactive” because they allow the timing, order, and conditions governing presentation to vary depending on input from the end-user.
In a typical DVD-Video playback setting, user input is communicated to the playback device via either a remote control (for a set-top DVD-Video player) or a computer mouse and keyboard (for a DVD-ROM drive connected to a computer). The user responds to onscreen prompts or menus (lists of possible options) by pressing keys or clicking the mouse. The playback path through the material available to be played is altered according to the choices or “navigation” of the user.
When presenting DVD-Video program material, a DVD playback device works with two basic categories of data to create the experience of the end-user, presentation data and logical data. Presentation data is the data that is actually seen or heard: the video, audio, graphics and text. The basic unit of presentation data in DVD is a Video Object (VOB), stored in a VOB file. Logical data is information about the order and conditions under which presentation data is presented. Logical data defines the way the content is organized, and also the way in which user input will affect the navigational flow through the presentation data. The basic unit of logical data in DVD is the Program Chain (PGC), defined in an IFO file. The presentation data seen (and heard) by the end-user results from the player following the instructions of the logical data (as well as user input from the remote control). Together, the presentation data and logical data for a given selection on the disc (i.e. a feature film, short film, or music video, as well as associated menus) are stored on the DVD in a set of files referred to as a Video Title Set (VTS). The VOBs used in each VTS are collectively contained in that VTS's Video Object Set (VOBS). The details of the various aspects of the DVD storage means and protocol are described more fully in “DVD specification for Read-Only Disc, Physical, File Format and Video Specifications”, DVD Consortium, 1997, which is hereby incorporated by reference in its entirety.
The process of creating interactive multimedia is generally referred to as “authoring.” Authoring is usually accomplished using one or more software applications running on a computer. In DVD-Video authoring, a disc or collection of discs that are created to be a single unit is commonly referred to as a “DVD title.” The authoring work in progress on a given title is commonly referred to as a “project.”
The heart of authoring is the defining of the logical data used to structure the playback of presentation data, such as defining the “user interface” (e.g. menus) used to navigate the program, the choices offered to users during playback, and the response of the playback device to user input. During this process, the project's presentation data is normally stored on a hard-drive where it is accessible—locally or via a network—to the authoring system. This allows the author to review the effects of authoring decisions on the way in which the program material is presented.
During the process of defining a project's logical data, the presentation data to which the logical data refers may be in any file format supported by the authoring software, and may be stored at any accessible location. In a project using multiple video clips, for instance, the source file for one clip might be an AVI file stored on the authoring system's internal hard-drive, for another it might be an MPEG-2 file on an external hard-drive, and for a third it might be a QuickTime file accessed from a server over a network.
Each authoring program has its own method of keeping track of the location and format of the presentation files used in a given project, and also keeping track of the logical data decisions that are made during authoring. One such approach is AuthorScript, developed by Sonic Solutions and used in several of its authoring programs. Other approaches are described, for example, in International Patent Application WO 99/38098, published Jul. 29, 1999, and U.S. Pat. No. 6,023,713, both of which are hereby incorporated by reference. In the AuthorScript approach, an AuthorScript (.AS) file is created by the authoring program to store both “structure” information related to a project's logical data, and “asset” information about a project's presentation data. Further aspects relating to the production of interactive optical media are described, for example, in International Patent Application WO 96/15500, May 23, 1996, which is hereby incorporated by reference.
When an existing project is “opened” in an AuthorScript-based authoring program, the AS file is read and the asset information in it is used to locate the source files of the presentation data. The structure data, meanwhile, is used to restore the project's logical state. As the project is edited, changes are stored in the .AS file, making an up-to-date record of the author's progress on the project.
At the end of the authoring process, when all the decisions regarding logical data are finalized, the project is formatted for delivery on a DVD. The formatting software reads the .AS file, evaluates the information therein, and carries out a series of operations that convert the project's current state into a form that is playable from a DVD-Video playback device.
In terms of presentation data, the process first involves locating the various source files referenced in the .AS file and, where necessary, converting those files to “elemental streams,” which are files in the formats used by DVD-Video for the various types of presentation media (e.g. video source files that are not already in the MPEG-2 video format are converted to that format). This may involve “transcoding” of one or more video files (e.g. a complete feature film) from one format to another. In some cases, it may also involve “compositing” several distinct components found in separate files into a unified whole. Compositing is particularly common in the case of menus, which often involve a number of visual elements that reside in different files during the authoring process.
Once the elemental streams exist in the appropriate file formats for use in DVD, they can then be multiplexed together into the Video Object (.VOB) files that are used by a DVD playback device. The logical data created in authoring is also organized into a set of files (.IFO) that can be read and interpreted by a playback device designed to play back discs in the DVD-Video format. Then a “disc image” is written that embodies the entire directory structure and data files that will appear on the final disc, with the logical and presentation files all residing in a VIDEO_TS directory (the “DVD-Video zone”), from which they can be read by a DVD-Video playback device.
A disc image is the source for all the DVDs that are made of a given title, whether replicated in a DVD plant or recorded onto a recordable DVD medium. However, the disc image itself cannot be opened as a project in a DVD-Video authoring program. A DVD-Video disc, therefore, is not functionally equivalent to the project from which it was made. However, AuthorScript incorporates a set of “OpenDVD” functionalities that allow revisions to a DVD title to be accomplished entirley with materials stored on the DVD itself, as is described in commonly assigned U.S. patent application Ser. No. 10/123,816, filed Apr. 15, 2002, which is hereby incorporated by this reference. This means that the files (the .AS file and the source assets) originally used to create a disc image need not be available when revising the title. Once a DVD title has been revised, the project may be written back to the disc. However, due to the size of VOB files, a simple transfer of all the material to the hard-drive of the system running the authoring software and then back to the rewritable disc requires significant space on the hard-drive and is generally very time-consuming.